erts_alloc_config

MODULE

erts_alloc_config

MODULE SUMMARY

Configuration tool for erts_alloc

DESCRIPTION

Note

erts_alloc_config is currently an experimental
tool and might be subject to backward incompatible
changes.

erts_alloc(3) is an
Erlang Run-Time System internal memory allocator library.
erts_alloc_config is intended to be used to aid creation
of an erts_alloc(3)
configuration that is suitable for a limited number of runtime
scenarios. The configuration that erts_alloc_config
produce is intended as a suggestion, and may need to be
adjusted manually.

The configuration is created based on information about a number
of runtime scenarios. It is obviously impossible to foresee every
runtime scenario that can occur. The important scenarios are
those that cause maximum or minimum load on specific memory
allocators. Load in this context is total size of memory blocks
allocated.

The current implementation of erts_alloc_config concentrate
on configuration of multi-block carriers. Information gathered
when a runtime scenario is saved is mainly current and maximum use
of multi-block carriers. If a parameter that change the use of
multi-block carriers is changed, a previously generated
configuration is invalid and erts_alloc_config needs
to be run again. It is mainly the single block carrier threshold
that effects the use of multi-block carriers, but other
single-block carrier parameters might as well. If another value of
a single block carrier parameter than the default is desired, use
the desired value when running erts_alloc_config.

A configuration is created in the following way:

Pass the +Mea config
command-line flag to the Erlang runtime system you are going
to use for creation of the allocator configuration. It will
disable features that prevent erts_alloc_config from
doing its job. Note, you should not use this flag
when using the created configuration. Also note that it is
important that you use the same
amount of schedulers
when creating the configuration as you are going the use on
the system using the configuration.

Run your applications with different scenarios (the more
the better) and save information about each scenario by calling
save_scenario/0.
It may be hard to know when the applications are at an (for
erts_alloc_config) important runtime scenario. A good
approach may therefore be to call
save_scenario/0
repeatedly, e.g. once every tenth second. Note that it is
important that your applications reach the runtime scenarios
that are important for erts_alloc_config when you are
saving scenarios; otherwise, the configuration may perform
bad.

When you have covered all scenarios, call
make_config/1
in order to create a configuration. The configuration is
written to a file that you have chosen. This configuration
file can later be read by an Erlang runtime-system at
startup. Pass the command line argument
-args_file FileName
to the erl(1) command.

The configuration produced by erts_alloc_config may
need to be manually adjusted as already stated. Do not modify the
file produced by erts_alloc_config; instead, put your
modifications in another file and load this file after the
file produced by erts_alloc_config. That is, put the
-args_file FileName
argument that reads your modification file later on the
command-line than the
-args_file FileName
argument that reads the configuration file produced by
erts_alloc_config. If a memory allocation parameter
appear multiple times, the last version of will be used, i.e.,
you can override parameters in the configuration file produced
by erts_alloc_config. Doing it this way simplifies
things when you want to rerun erts_alloc_config.

Note

The configuration created by erts_alloc_config may
perform bad, ever horrible, for runtime scenarios that are very
different from the ones saved when creating the
configuration. You are, therefore, advised to rerun
erts_alloc_config if the applications run when the
configuration was made are changed, or if the load on the
applications have changed since the configuration was made. You
are also advised to rerun erts_alloc_config if the Erlang
runtime system used is changed.

erts_alloc_config saves information about runtime scenarios
and performs computations in a server that is automatically
started. The server register itself under the name
'__erts_alloc_config__'.

make_config/1 uses the information previously saved by
save_scenario/0
in order to produce an erts_alloc configuration. At
least one scenario have had to be saved. All scenarios
previously saved will be used when creating the
configuration.

If FileNameOrIODev is a string(),
make_config/1 will use FileNameOrIODev as a
filename. A file named FileNameOrIODev is created and
the configuration will be written to that file. If
FileNameOrIODev is an
io_device() (see the
documentation of the module
io), the configuration
will be written to the io device.